[sdiy] voltage controlled slew with transistors

[Oren Leavitt]

The Serge Voltage Controlled Slope (VCS) is a good example.

https://pugix.com/synth/wp-content/uploads/2012/12/cgs75_vcs.pdf

Jürgen Haible's VC HADSR is another

http://jhaible.com/legacy/tonline_stuff/jh_vc_hadsr.pdf

- Oren


On 10/13/21 8:08 PM, Chris McDowell via Synth-diy wrote:
> Howdy list,
>
> I'm working on an envelope design, and currently using an LM13700 for the "make ramps" part, but wondering if anyone knows of some resources or reasonable strategies for replacing that with a few transistors? I've been playing in LTSpice trying to see how a discrete OTA arrangement can do it (and I know it can) but I don't understand it enough to make it a 1 pole filter cell instead of a VCA. I've got a long tailed pair with tail current control, and I understand how we can take the difference of the collector voltages to get a VCA, but not how to keep it a current output for charging a cap. obviously have some kind of hole in my understanding! :) any pointers would be much appreciated.
>
> Cheers,
> Chris
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